Now you iDevicers building themes can move full steam ahead with the 4.1 complete theming.
On Iphone 4 running 4.1 you need to name your png exactly like this
Do not put a @2x at the end of it
The size is 640×960
Transfer this to your com.apple.springboard folder inside your theme (same place as always)
If it is already there just take the @2x off the end of it
Use ssh or ifile and navigate to User/Library/Caches
Then scroll down until you see this file
delete this file then respring
its ok its just a cache it will reappear after you respring
and you should see the background you made
On iphone 3gs this will work the same way you might have to resize it to 320×480
Peep the video below to see how it’s done below.